Apparatus and methods for mitigating impairments due to central auditory nervous system binaural phase-time asynchrony

ABSTRACT

Pathological binaural phase time delay (PBTD) asynchrony is measured at a variety of frequencies and speech stimuli to develop a BPTD profile for a subject. A corrective device ( 600, 1000 ) is designed to apply clinical PBTD to compensate for the subject&#39;s pathological BPTD. An electronic device ( 500 ) is used to measure the subject&#39;s ability to comprehend words at a variety of relative time delays between ears to estimate the ideal overall relative time delay. The optimal relative phase shift at a variety of frequencies is also measured. An electronic device ( 600 ) may be used to correct the pathological BPTD by delaying sound in different frequency bands differently to the target ear, according to the BPTD profile, or a passive filtered earplug ( 1000 ) may be used to correct smaller amounts of BPTD.

RELATED APPLICATIONS

This application is a divisional of copending U.S. patent applicationSer. No. 10/110,035 filed Apr. 2, 2002, which is incorporated byreference herein.

FIELD OF THE INVENTION

The present invention relates to apparatus and methods for diagnosing,quantifying, and correcting for human central auditory nervous system(CANS) impairment, and in particular binaural phase time delayasynchrony.

BACKGROUND OF THE INVENTION

Preliminary studies indicate an important connection between thebinaural synchronization of the central auditory nervous system (CANS)and gross, fine and oral motor function. A binaural phase time delay(BPTD) is defined herein as a synchronization disruption (delay) inphase and time of the auditory input signals to the two ears. Two typesof BPTDs have been defined by the investigators: pathological BPTDswhich are “built-in” to a person's CANS, as is the case with a personwith neurological injury or disease process, and clinical BPTDs whichare induced in a person's CANS using an external device, to compensatefor a pathological phase time delay.

A BPTD is a combination of a phase shift and a time delay. For puretones, a specific phase shift results in a specific time delay. Forexample, at 1000 Hz a 180° phase shift results in a 0.5 ms time delay.However for speech and other multi-frequency sounds, one specific timedelay would result in several different frequency-dependent phaseshifts. Note that a time delay can be much larger than the maximum phaseshift for a given frequency.

Operationally, binaural interaction of the CANS requires a person's twoears to integrate dichotic signals separated in time, frequency, and/orintensity. The brain stem is crucial for binaural interaction ofacoustic stimuli. Stillman (1980) has emphasized that precise timing ofexcitatory and inhibitory inputs to each cell along the auditory pathwayis critical if each cell is to respond in an appropriate manner. Oertel(1997) has also studied the effects of timing in the cochlear nuclei.The superior olivary complex is an important relay station of theascending tract of the CANS and is critical for binaural listeningcapabilities. It is this cross correlation behavior of the two ears thatafford the selective listening capability in noisy environments, and theability to spatially localize sound sources. However, it has been shownthat signals from the two ears must have synchronized arrival times forbinaural cells to be activated in the superior olivary complex. Adelayed signal received from one ear negates a binaural response. Thereis evidence that the synchronization of auditory stimuli is importantabove the superior olivary complex, at the levels of the brainstem andcerebral cortex.

In individuals (adults and children) with an impaired CANS, apathological BPTD has been observed between the two ears which is, insome cases, quite large (15-20 msec).

The pathological BPTD not only decreases speech intelligibility incomplex listening environments, but also (somewhat surprisingly)degrades motor (gross, fine, oral) and visual performance. Furthermore,a clinically-induced BPTD, designed to compensate for the pathologicalBPTD in a subject, significantly improves the speech intelligibility,gross and oral motor function of the subject.

It is well known that a head injury frequently results in generalizedtrauma to the brainstem and to higher cortical mechanisms which includethe central auditory nervous system, resulting in central auditoryprocessing function abnormalities. Other conditions such as sensoryintegration problems, speech and language delays, hearing impairment,learning disabilities, multiple sclerosis, Parkinson's Disease, autism,stuttering, developmental delays, central auditory processing disorders,psychological disorders, and neurological disorders have been associatedwith CANS dysfunction. Individuals with central auditory processingproblems often demonstrate difficulty comprehending and rememberingauditory information. In addition, these individuals have particulardifficulty attending to auditory information in the presence of auditorydistractions.

In some traumatic brain injuries and other debilitative neurologicalbrain disorders, the processing of information by the central auditorynervous system is impaired and affects comprehension and recall ofauditory information. Operationally, the central auditory nervous systemtypically receives auditory information from both ears and integratesthe input received, even though the acoustic signals received by theears may be somewhat separated in time, frequency, and/or intensity.Such binaural integration by the central auditory nervous system may besubstantially provided in the brain stem. Further, it has been observedthat the precise timing of excitory and inhibitory inputs to cells ofthe central auditory nervous system can affect these cells' behaviorwith regard to responding appropriately. In particular, it has beenshown that auditory signals from both ears must have a relativelysynchronized arrival time for certain binaural cells to be activated inthe superior olivary complex. Thus, a delayed (e.g. millisecond)response from one ear can impair the integration of a binaural response.This is not reflected in the function of the inner ear.

However, an individual with a peripheral hearing loss may also have CANSdysfunction or a mechanical effect that creates a disruption of thesynchrony between the two ears.

Behavioral and physiological (auditory brainstem response, middlelatency response, cortical evoked potentials and mismatched negativity)methods have been employed to measure time parameters of the centralauditory nervous system. Previous studies, however, have only analyzedthe relationship of timing differences with respect to variouspathologies (e.g. a latency in response has occurred). In particular,the development of tests quantifying the changes in auditory inputbetween a subject's ears has been solely used as a diagnostic procedurefor identifying a central auditory processing dysfunction. Since theanatomy of the brain stem indicates links between binaural signalprocessing and integration and motor control, it is not surprising thatdisorders of the central auditory nervous system often affect otherfunctions such as sensory perception, integration, fine and gross motor,oral motor and visual processing. Accordingly, it would be useful toprovide procedures and a diagnostic device that more accurately identifyand quantify binaural processing disorders and the relationship of suchdisorders to other neurologically-based abnormalities. Further, it wouldalso be useful to have a device that subjects manifesting binauraldysfunction-derived disorders can utilize to enhance day-to-dayactivities so that there may be enhanced speech understanding andrecognition, concentration, gross motor movements (e.g. walking), finemotor movements (e.g. writing), oral-motor movement (e.g. speaking) orvisual function.

The following references are relevant to the present invention:

-   U.S. Pat. No. 5,434,924 to Jampolsky; “Two New Methods for    Assessment of Central Auditory Function in Cases of Brain Disease,”-   Matzker, Annals Of Otology,-   Rhinology, & Laryngology 68,1185-1196,1959; “Auditory and Vestibular    Aberrations in Multiple Sclerosis,” Noffsinger et al, Acta    Otolaryngologica, 303 (Suppl.), 1-63,1972;-   “Assessing Central Auditory Behavior in Children,” Willeford,    Central Auditory Dysfunction, 43-72,1977; and-   Westone Style & Num; 47 Soft PVC Custom Molded Ear Plug with Quiet    Tech Int. Filter.

A need remains in the art for apparatus and methods for diagnosing,quantifying, and correcting for binaural phase-time delay asynchrony.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide methods fordiagnosing, quantifying, and correcting for binaural phase-time delayasynchrony.

The ideal overall relative time delay portion of the BPTD for a subjectis measured by separating the high and low frequencies of a variety ofwords, and time shifting one of the two components relative to theother. The subject's comprehension of the words will be highest or bestat that subject's ideal relative time delay. Time delays can also bemeasured by inducing a pre-selected time delay of monosyllabic orbisyllabic words in one ear relative to the other ear in the presence ofmulti-talker babble.

A phase analysis test (PAT) measures the appropriate binaural phaseshift at a variety of frequencies by assessing the subject's ability todiscriminate pure tones from narrow band noise centered in frequencyaround the target tone. The BPTD device can be used as a diagnostic toolin this situation. The BPTD device is capable of interfacing withstandard audiometers to generate two types of stereo signals. One is thetarget signal that is comprised of a pure tone presented to both earswith a relative phase difference of “q” degrees between the target tonechannels. The narrowband noise signal is also processed by the BPTDdevice on a stereo basis to generate a relative phase difference of “f”degrees between the two narrowband noise channels. The BPTD device thenmixes these two types of signals together by performing a weightedsummation operation, and the output can then be presented to thesubject. The weighting value on the summation operation is used to varythe signal-to-noise power ratio between the target signal and the noise.Since the resulting output signal is a combination of these two signaltypes it may be called the “S_(q)N_(f)” output signal.

The BPTD device can implement a variety of combinations of “q” and “f”parameters for research, diagnostic, and accommodative purposes. The PATtest is produced by generating SqNq (q=f) output signals over a range oftone frequency and phase (q) values. For each frequency and phasecombination the amplitude of the target tone is varied in a procedure toestablish the minimum target strength level needed to hear the targetsignal in the presence of narrowband noise. For diagnostic purposes,threshold results from a specific SqNq at various frequencies representthe baseline condition. Normative threshold measures for each targetfrequency and phase value tested will be used to determine atypicalphase results for various frequencies.

The optimal phase value for a given operating frequency foraccommodative purposes is the one in which the tone is heard at thelowest hearing threshold value. An operator interface allows the BPTDdevice to be used to systematically collect the optimal phase valuesover the range of test frequencies.

The PAT test also includes the synthesis of all of the phase informationto form a phase correction filter as illustrated in FIG. 9 and discussedin greater detail below. The BPTD device also has the capability ofimplementing the phase correction filter in real-time. With thecorrection filter in place, a speech stimulus can be used to repeat thephase analysis paradigm described above. However, since speech is afrequency rich stimulus, the narrowband noise is replaced with noisethat has a broader frequency profile, such as broad-band or white noise.As before, a procedure for determining the minimum hearing threshold forwhen the target speech signal is heard above the broad-band noise signalis implemented. Comparisons can then be made to the situation where thecorrection filter is not in place and performance improvements can beverified. It should also be noted that the phase correction filter canbe compared or combined with optimal time delay parameters (such asthose obtained from the Delayed Binaural Fusion Test). Furthermore, theBPTD device is capable of implementing this hearing threshold approachto investigate and diagnose time delay parameters such as thoseconsidered for the Delayed Binaural Fusion Test.

An electronic device is used for diagnosing and measuring the phase andtime portion of BPTD, and verifying the best overall relative time delayfor the subject. An operator controls the relative time delay and phasedelay applied to the subject's ears via an operator interface. The testset up considers one frequency (tone) at a time and applies the selectedphase shift (and/or time delay) to whatever frequency is applied. Theoperator interface may include a keypad to enter control signals, and adisplay to show which control signal is being applied. Control signalsset the amount of phase shift to be applied. The relative time delayshifter applies the overall relative time delay, and the phase shifterapplies the phase shift.

A real time, active, digital signal processing electronic device is usedfor correcting BPTD, once it has been measured in the testing phase.Equivalent analog devices could also be used, but digital devices aremore practical. In general, only one of the devices will be used, sincesound is typically delayed to the same ear at every frequency.

Sound enters a microphone, which turns the sound into an analogelectrical signal representing the sound. The signal is amplified by apreamp, and is digitized in an analog to digital converter (ADC). Adigital signal processor (DSP) operates much as the test deviceoperated, applying an overall relative time delay and a phase shiftprofile. A digital to analog converter (DAC) converts the processedsignal back to an analog signal, an amplifier filters and amplifies thesignal, and a microphone turns the signal into an audio signal to bedelivered to the ear of the subject.

The BPTD applied by the DSP is programmed according to the overallrelative time shift and the phase shift versus frequency profileobtained in the testing phase. The BPTD profile is unique for eachsubject. The DSP can be reprogrammable, via a control signal, so it canbe optimized for the wearer in actual use. Note that other hearing aidprocessing (compression or the like) may also be incorporated into theDSP if desired. Amplitude changes may also be implemented. In addition,the BPTD profile used may change with the kind of background noisedetected by the device, or the type of activity the subject isperforming.

A physical filter (a passive earplug) may alternatively be used forcorrecting BPTD. A physical device in the ear can delay the sound in theear, and can delay different frequencies differently, as an electronicdevice does. The passive earplug induces a BPTD to sound entering theear by altering the propagation time of the acoustic waves. The primarymethod of delaying an acoustic signal in this manner is through the useof ducting, through which the signal propagates. The velocity ofpropagation of sound in air is approximately 331 meters per second, andthe length of the ducting in the ear canal is about 10 cm (ducting alongan eyeglass frame can be longer). Thus the time delay applied by apassive device in the ear canal is on the order of 30 us, correspondingto a phase shift of about p/3 at 5000 Hz. This time delay may beincreased by about a factor of two by using a fluid rather than air inthe ducting. In addition to the overall delay created by ducting, thefrequency response of the earplug may also be tuned by using acousticalfilter elements.

Standard elements include chambers, Helmholtz resonators, and dampers.In addition, other acoustic elements such as horns, collectors, domes,trumpets, and resonators may be used.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a flow diagram showing a set of diagnostic procedures fordiagnosing and quantifying pathological binaural phase time delay (BPTD)in subjects;

FIG. 2 is a flow diagram showing the conventional tests performed inFIG. 1, in more detail;

FIG. 3 is a flow diagram showing the phase analysis tests performed inFIG. 1, in more detail;

FIG. 4 is a flow diagram showing the delayed binaural fusion testsperformed in FIG. 1, in more detail;

FIG. 5 is a block diagram of an electronic device for diagnosing andmeasuring BPTD;

FIG. 6 is a block diagram of an electronic device for correcting BPTD;

FIG. 7 is a more detailed block diagram of the digital signal processor(DSP) of FIG. 6;

FIG. 8 is a flow diagram showing the process accomplished by the DSP ofFIG. 6;

FIG. 9 is a diagram showing an example of the correction accomplished inthe BP block of the DSP of FIG. 7;

FIG. 10 is a cutaway side view of a physical filter for correcting BPTD;and

FIGS. 11-19 are charts illustrating test results for an embodiment ofthe present invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a flow diagram 100 showing a set of diagnostic procedures fordiagnosing and quantifying pathological binaural phase time delay (BPTD)in subjects. The tests may be performed in any order, but the ordershown is the most logical, for reasons described below.

The test routine begins with step 102. In general it will be desirableto perform a series of conventional hearing tests 104 on the subjectfirst, in order to determine whether other hearing problems or centralauditory processing problems exist. These tests are shown in more detailin FIG. 2. Next, a series of pure tone phase analysis tests 106 areperformed to determine the optimal clinical phase shift at a variety ofsound frequencies.

The subject's ability to identify a tone out of noise centered aroundthe tone and the resultant threshold is assessed at a variety ofrelative phase shifts between ears, and at a variety of frequencies, anda profile of the subject's phase shift frequency profile is generated.The frequency profile will be used to complement a phase correctionfilter. With this filter in place, speech stimuli can be used as atarget in a similar fashion with broad band noise. These tests are shownin more detail in FIG. 3.

Finally, a series of delayed binaural fusion tests 108 are performed.These tests assess comprehension of words at a variety of relative timedelays between ears, and at a variety of frequencies. Again the resultsof this test are used to develop the subject's time delay versusfrequency profile. This test is matched up to the pure phase test tocomplete the BPTD profile. This test also allows for testing of relativeshifts greater than one wavelength, which cannot be done with tones.FIG. 5 shows an embodiment of an electronic device that assists inperforming the tests of FIGS. 3 and 4.

In step 112, the results for the subject are compiled in a database. Ifthe pathological BPTD for the subject is significant, this database isused to design an electronic filter (see FIG. 6) or a physical filter(see FIG. 7) to apply compensating clinical BPTD to the subject's ears.In step 120 the test routine is complete.

FIG. 2 is a flow diagram showing conventional tests 104 (FIG. 1) in moredetail. The conventional tests 104 start at step 202. In general thesetests include a pure tone evaluation 204 to evaluate hearing loss atvarious frequencies. A central auditory processing evaluation 206 isperformed, and various electro-physiological assessments 208 areperformed as well. Other assessments 210 may be added. The conventionaltests end at step 212.

Central auditory processing evaluation 206 may include (but is notlimited to) such tests as: Willeford central auditory test battery;Dichotic digits test; Ipsilateral/contralateral competing messages;Synthetic sentence identification with contralateral competing messages;Masking level differences; Auditory duration patterns; Speech-in-noise;Pediatric speech intelligibility test; segment altered CVCs; pitchpatterns; dichotic chords; compressed speech, with and withoutreverberation.

Electro-physiological assessments include such tests as: ABR; Middlelatencies; Late latencies; P300; Mismatched Negativity. Binauralinteraction components will also be calculated. Sinceelectrophysiological measurements use various latency classifications ormarkers, this information may yield added information to the diagnosisand quantification of auditory asynchronies.

FIG. 3 is a flow diagram showing the pure tone phase analysis test 108(FIG. 1), according to the present disclosure. A device such as thatshown in FIG. 5 may be used in this test. This test assesses thesubject's ability to discriminate pure tones from narrow band noisecentered around the tone. The pure tone and the noise are presented toeach ear at a different phase (giving a relative phase shift or clinicalBPTD). Thresholds are obtained for each tone at varying phase shifts. Inthe preferred embodiment, a relative phase shift is selected, and theamplitude of the tone is increased until the subject can pick it out ofthe noise. The optimal phase shift is the phase shift that produces thesmallest amplitude hearing threshold.

The test starts at step 302. Narrow band noise and pure tones areapplied to both ears in step 304. In outer loop 314, frequencies arestepped through, for example from 500 Hz to 12000 Hz (step 308). Ininner loop 316 phase shifts of the pure tone between the two ears arestepped through for each frequency, for example 30, 60, 90, 120, and 180degrees (step 310). These two loops can be exchanged if desired.

Step 312 tests the subject's threshold for the pure tone at thatfrequency and phase shift, and stores the result, for example in atable. Step 318 determines the optimal relative phase shift between earsat each tested frequency, by determining at which phase shift the tonewas heard best (at the lowest amplitude) over the background noise, foreach frequency, compared to normal phase shift function. Thus a clinicalphase shift versus frequency profile is developed to compensate for thephase portion of the subject's pathological BPTD. The phase analysistest ends at step 320. This test procedure is also used with speechstimuli as the target signal using a phase correction filter and broadband noise.

FIG. 4 is a flow diagram showing delayed binaural fusion test 112 (FIG.1). This test measures the subject's ability to comprehend words(preferably bisyllabic) at various time delays between the two ears.Thus, it provides information regarding timing differences between thetwo ears and adds information beyond the phase analysis test. Examplesof the tests done are given below.

The test starts at step 402. High Low Frequency Lags Test 404 testscomprehension of a series of bisyllabic words separated into twofrequency components (e.g. a high frequency component from 1900-2100 Hzand a low frequency component from 500-770 Hz) presented at a variety ofrelative time delays to the ears. The purpose of step 404 is todetermine whether a significant impairment due to CANS binauralphase-time asynchrony exists for the subject. For a person without thistype of impairment, the change in relative time delays does notsignificantly affect comprehension—the CANS can account for the changes.In addition, the best comprehension occurs for the case of no relativetime delay, as would be expected. For a person with significantimpairment due to CANS binaural phase-time asynchrony, however,different relative time delays result in very different levels ofcomprehension, and the best comprehension occurs at a relative timedelay other than zero. If the results of step 404 indicate that aCANS-BPTD impairment exists, step 408 determines the optimal time delayfor the subject.

Each word is presented to both ears, the high frequency portion of theword going to one ear and the low frequency portion of the word going tothe other ear. The relative time delay between the ears is changed foreach word, and a variety of words are used at each relative time delay.The words are generally bisyllabic, familiar to most people, and theemphasis is placed on both syllables equally (e.g. woodwork, bedroom,inkwell). For example, a series of 120 words may be used, divided amongthe selected relative time delays. Other speech stimuli can be usedalong with other novel ways to split or partition out speech segments. Acomputer program for sequentially selecting the words and setting therelative time delay for each word makes this process much easier. Theprogram may also provide a score sheet for entering whether each wordwas correctly identified, and computing the correct averages at eachphase shift.

Steps 404 and 408 zero in on the ideal clinical relative time delay,because it is difficult for a subject with CANS-BPTD impairment tounderstand a word if the high and low frequency components are notcorrectly time shifted relative to each other, or when they are laggedwhile being embedded in noise or speech-babble. In other words, auditorydiscrimination improves with an induced time delay in one ear forindividuals with a CANS dysfunction. Other speech modifications using alag paradigm may be used for identifying and quantifying asynchronies.

The described tests are scored by computing the percentage of correctresponses given by the subject at each relative time delay, and eachstep refines the results of the previous step. A software program forsequentially selecting the words and setting the relative phase shiftfor each word makes this process much easier. The program also providesa score sheet display for entering whether each word was correctlyidentified, and computes the correct averages at each phase shift whenthe test is completed. The phase shifts tested may be selected in viewof the ideal overall clinical phase shift that was computed at the endof the pure tone or speech phase test of FIG. 3, in order to make thistest more efficient.

High-low frequency lags test 404 tests comprehension of a series ofwords at (for example) relative time delays of 5, 10, 15, and 20 msec tothe left and right ears. The best comprehension level might be achievedat, for example, 5 msec time delay to the right ear. Incremental DBFTtest 408 then tests comprehension of a series of words at relative timedelays of 2.5, 5, and 7.5 msec (assuming a 5 msec delay gave the bestresults in step 404). The best comprehension level might be achieved at,for example, 7.5 msec time delay. Those skilled in the art willappreciate that further fine tuning can be accomplished with smallerrelative time delays using the BPTD diagnostic device, if desired.

Zero delay word lists test 410 then verifies the results from steps 404and 408 by testing comprehension at the selected relative time delay,using a device such as that shown in FIG. 5.

Step 412 stores the optimal time delay selected by the previous steps.The test ends at step 414. A correction device such as that shown inFIG. 6 may now be designed, by combining the results of the PhaseAnalysis Test shown in FIG. 3 and the DBFT test shown in FIG. 4.

FIG. 5 is a block diagram of an electronic device 500 for diagnosing andmeasuring the phase and time portions of BPTD, and for verifying thebest overall relative time delay for the subject (see FIG. 4, step 408).An operator controls the relative time delay and phase delay applied tothe subject's ears via an operator interface 502. The test setup shownin this figure tests one frequency (tone) at a time and applies theselected phase shift to whatever frequency is applied. The steps of thephase shift test are shown in FIG. 3.

Operator interface 502 may include, e.g. a keypad to enter controlsignals, and a display to show which control signal is being applied.Control signals 504 set the amount of relative time delay and phaseshift to be applied by digital signal processor 510. Sound 506 isdigitized via channels 507 and 508 (or only one microphone may be used).Relative time delay shifter 512 applies the overall relative time delayper control signals 504, and phase shifter 514 applies the phase shift.The output of block 510 is delivered to the left ear 522 of the subject520 via signal 516, to the right ear 524 of the subject via signal 518.

FIG. 6 is a block diagram of real time, active, digital signalprocessing electronic device 600 for correcting BPTD, once it has beenmeasured. Equivalent analog devices could also be used, but digitaldevices are more practical.

Sound enters microphone 602, which turns it into an analog electricalsignal representing the sound. The signal is amplified in preamp 604,and is digitized in analog to digital converter (ADC) 606. Digitalsignal processor (DSP) 608 operates much as test device 500 in FIG. 5operated, applying a time delay and a phase shift profile (see FIG. 7).Digital to analog converter (DAC) 610 converts the processed signal backto an analog signal, amplifier 612 filters and amplifies the signal, andmicrophone 614 turns the signal into an audio signal to be delivered tothe ear of the subject.

The BPTD applied by DSP 608 is programmed according to the BPTD versusfrequency profile obtained in the testing phase. It (the BPTD) is uniquefor every subject. As an option, the DSP 608 could be reprogrammable,via control signal 616, so it could be optimized for the wearer inactual use. Note that other hearing aid processing (compression or thelike) may also be incorporated into the DSP 608 if desired.

Furthermore, we have observed that BPTD's produce a very noticeableauditory effect in the presence of noise regardless of whether thesubject has CAP difficulties or not. The fact that the implementation ofBPTD parameter changes produce differences in target speech (speechstimuli) perceived loudness in the presence of masking noise indicatesthat BPTD's have the potential for enhancing hearing aid performance.

In addition, the BPTD profile used may change with the kind ofbackground noise detected by the device. A different BPTD profile may beused when the wearer is in a noisy environment, for example, or fordifferent actions, as when the wearer is walking rather than sitting andwriting.

FIG. 7 is a more detailed block diagram of DSP 608 of FIG. 6. BPTDcontrol block 702 (via control signal 616, if used) controls the overalltime delay and the phase shift profile applied to the sound signal. TDcorrection block 704 applies the overall time delay. BP correction block706 applies a phase shift profile to the sound signal. See FIG. 9 for anexample of a phase shift profile.

FIG. 8 is a flow diagram showing the process accomplished by the DSP 608of FIG. 6. The audio input signal is applied in step 802. In step 804,the overall time delay is applied. In step 806, the phase profile isapplied. In step 808 other processing is accomplished, if desired(compression or the like). The corrected output signal is output in step810.

FIG. 9 is a diagram showing an example of the phase shift profilecorrection accomplished in BP block 706 of DSP 608 of FIG. 7. Dottedline 902 indicates linear phase, and solid line 904 indicates the phaseprofile after the phase corrections. q₁, q₂, and q₃ indicate phaseshifts at specific frequencies f1, f2, and f3 respectively. Note that adifferent phase shift is applied at each frequency, and that positiveand negative phase shifts may be applied. Of course, the overall timedelay applied by block 704 means that, overall, the time delay plus thephase shift will be positive.

FIG. 10 is a cutaway side view of a physical filter (a passive earplug)for correcting BPTD. A physical device in the ear can delay the sound inthe ear, and can delay different frequencies differently, as electronicdevice 600 (in FIG. 6) does. However, a physical device is capable ofmuch smaller time shifts, and the control at different frequencies isfar less precise. Since the physical device is much cheaper and does notrequire batteries, it is the preferred device is some cases, for examplewhen a small phase shift or delay is required, and the phase shiftrequired doesn't vary much at various frequencies. The physical filteris also smaller and more convenient.

Passive earplug 1000 induces a BPTD to sound entering the ear byaltering the propagation time of the acoustic waves. The primary methodof delaying an acoustic signal in this manner is through the use ofducting 1002, through which the signal propagates. The velocity ofpropagation of sound in air is approximately 331 meters per second, andthe length of the ducting in the ear canal is about 10 cm (ducting alongan eyeglass frame can be longer). Thus the time delay applied by apassive device in the ear canal is on the order of 30 us, correspondingto a phase shift of about p/3 at 5000 Hz. This time delay may beincreased by about a factor of two by using a fluid rather than air inducting 1002. For example, the velocity of sound in iodine is around 108m/s.

In addition to the overall delay created by ducting 1002, the frequencyresponse of earplug 1000 may also be tuned to some degree by usingacoustical filter elements 1004 (limited by space available). Standardelements include chambers, Helmholtz resonators, and dampers. Inaddition, other acoustic elements such as horns, collectors, domes,trumpets, and a resonator may be used.

A direct analog may be made to an electrical BPTD system such as thatshown in FIG. 6, with Helmholtz resonators and expansion chambers usedto create filter characteristics. The number of cavities relates to theorder of filter that can be designed.

In general, the phase time delay provided by passive element 1000 isdependent on the length of the auditory ducting 1002 within the plug,the diameters and locations of the cavities (side branch chambers 1008or expansion chambers 1006) and the working fluid in the ducting.

While the exemplary preferred embodiments of the present invention aredescribed herein with particularity, those skilled in the art willappreciate various changes, additions, and applications other than thosespecifically mentioned, which are within the spirit of this invention.

APPENDIX A Examples of Testing Procedures

TABLE 1 Delayed Biaural Fusion Test Table of Words List 1 List 2 List 3List 4 List 5 List 6 woodwork redbird doorbell sunset highway dishclothchalk- desktop racetrack bookmark doormat handbell board shortcakeplayground treetop meatball grandson padlock baseball icecream wildcatheadlight toothbrush northwest scarecrow lighthouse downtown shipwreckhardware hardhat hatrack armchair whitewash bullfrog flagpole mushroomhousework corncob windmill handshake hairbrush eardrop railroadhighchair tshirt pancake airplane football duckpond schoolbell bedspreadbedroom inkwell drugstore nightfall workshop bluejay iceberg keyholetoolbox stairway drawbridge daybreak birdnest hottub teabag beanbaggoldfish driftwood dirtbike mousetrap lightbulb horseshoe lefthandsidewalk farewell birdhouse sandbox farmhouse shirttail billboardbathtub pinwheel cowboy starfish snowball greyhound toothpick earthwormyardstick doghouse eyebrow oatmeal daylight iceskate eardrum cookbookbirthday snowman schoolboy bustop rainbow offshore blackboard stringbeanshoelace thumbtack treehouse swingset shortcut forehead dollhousehothouse carwash hotdog timeout cardboard lifeboat jailhouse footstool

TABLE 2 Delayed Binaural Fusion Test Time Delay Sequencing Table LaggingCondition List 1 List 2 List 3 List 4 List 5 List 6 Channel 1 0 5 10 1520 25 Low Freq. 2 25 0 5 10 15 20 Low Freq. 3 20 25 0 5 10 15 Low Freq.4 15 20 25 0 5 10 Low Freq. 5 10 15 20 25 0 5 Low Freq. 6 5 10 15 20 250 Low Freq. 7 0 5 10 15 20 25 Low Freq. 8 25 0 5 10 15 20 Low Freq. 9 2025 0 5 10 15 Low Freq. 10 15 20 25 0 5 10 Low Freq. 11 10 15 20 25 0 5Low Freq. 12 5 10 15 20 25 0 Low Freq.

APPENDIX B Clinical Results

Clinical results indicative of the efficacy of the present invention areprovided hereinafter. In particular, representative results will beprovided for the diagnostic effectiveness of the delayed binaural fusiontest (DBFT) and for the efficacy of binaural phase-time delay (BPTD)compensating devices as clinically demonstrated by subjects having BPTDimpairments, wherein the compensating device substantially alleviatedthe debilitating effects of such BPTD generated impairments.

Delayed Binaural Fusion Tests (DBFT)

The results of the preliminary studies presented below demonstrate theunderstanding of the significance and feasibility of the patentableapparatus and method. In brief, the inventor's research documents thatsubjects with normal CANS function demonstrate optimal BPTDs at 0 msec.In other words, their auditory systems function optimally when acousticstimuli have a matched-timed onset to the two ears. In contrast, thesepreliminary studies clearly demonstrated that subjects with CANSdysfunction show that matched-timed onset of acoustic signals (i.e., a 0BPTD) do not result in optimal auditory function. In fact, optimalauditory function can only be obtained when a BPTD is induced betweenthe two ears. The degree of the BPTD is quantified by DBFT results thatare specific to each individual. The following descriptions of thesepreliminary studies will clarify what is meant by a BPTD and how a BPTDis induced.

The first study assessed the effects of BPTDs on auditory performancefor individuals with both normal and atypical CANS function using theDBFT in a high-pass and low-pass frequency filtered format (404 in FIG.4)). This investigation concentrated on ascertaining the percentagechange in auditory discrimination ability of bisyllabic words presentedin a binaural interaction format at various msec lag times. A total of115 subjects from 12 to 58 years of age were included in this study.Forty subjects were included in the normal CANS function group and 75 inthe atypical CANS function group. The mean age for the normal CANS groupwas 25.74 with a range of 12 to 56. The mean age for the atypical CANSgroup was 20.3 years with an age range of 12 to 58 years. Selection foreach group was determined by the results obtained on the centralauditory processing (CAP) test battery. This battery included theCompeting Sentences, Filtered Speech, and Binaural Fusion Tests of theWilleford Central Auditory Test battery (Willeford, 1977), theIpsilateral/Contralateral Competing Sentence Test (IC/CST) (Willeford1985a, 1985b, Willeford et al., 1985; Willeford et al., 1994), SyntheticSentence Identification-Ipsilateral Competing Messages (SSI-ICM) (Jergeret al., 1974,1975; Speaks et al., 1965), Dichotic Digits (Musiek, 1983;Musiek et al., 1979; Musiek et al., 1979) and Masking Level Differences(MLD) (Noffsinger et al., 1972; Olsen et al., 1976). Using one-wayANOVAs, test performance showed significant differences between the twogroups as defined by performance on this test battery. A former study byBurleigh (1996) clearly showed significant differences between normal

CANS function and atypical CANS function groups when using this testbattery and agreed with these findings.

The low-pass and high-pass frequency filtered format, one version of theDBFT (404 FIG. 4), and shown in Table 1, was used to quantify inherentBPTDs between ears. Statistically significant differences in speechrecognition performance between normals and atypicals in the DBFT studyof 115 subjects were observed. Significant differences in percentperformance were also evidenced in all conditions for both ears exceptfor a left ear lag at a 15 msec delay. The reason for this decrease infunction for both normal and atypical groups at a 15 msec lag deservesfurther study. One can speculate that interaural timing for the left earmay reflect transfer of information at the level of the corpus callosum.

Further analysis showed that 78.67% of the atypical group showed a 20%or better increase in speech discrimination ability in noise withinduced or compensating

BPTDs as compared to the 0 msec-lag condition. For those with normalCANS function, only 35% showed 20% or better improvement with theimplementation of various lag times as compared to 0 msec lag. FIG. 11shows the percent of individuals who improved 20% or better for speechdiscrimination ability for both groups as compared to each subject's 0msec score.

Statistically significant differences in auditory discriminationperformance between normals and atypicals at 5 msec lag intervals areshown in FIG. 12. As demonstrated in this figure, significantdifferences in subjects who improved at least 20% from 0 msec wereobserved between groups for auditory conditions of 5 msec through 25msec lags as compared to a baseline of 0 msec (absence of a time lag).

Standard Passive Earplugs

Initial clinical exploration of BPTDs involved the use of commerciallyavailable noise reduction filters that were originally designed foroccupational safety. The specific earplug that has been used for thisstudy is designed to attenuate damaging sounds while maintaining theamplitude of conversational frequencies in order to perform routinetasks while wearing the earplug. It is primarily used for industrialpurposes. The earplug that was used for this portion of the clinicalstudy is made of polyvinylchloride in a half shell ear mold. Thisstandard filtered earplug was modified to get the following clinicaldata. Due to the non-specific design of this earplug, only a single timedelay was possible that was altered slightly by modifications to thelength of the ear mold portion of the plug. The current art regardingdiagnostics, as described earlier in this document, requires moreflexibility with design and materials to accomplish closer control ofand variations of the BPTDs. In particular it is evident that greatercontrol of BPTDs at targeted frequencies is needed based on thediagnostic results. In particular, to utilize the commercially availableearplug, we had to shorten the canal length in order to reduce theattenuation of the earplug while still providing a significant timedelay from the filter elements. By shortening the length of the earcanal we could use the hard surface of the external auditory meatusitself for frequency filtering. Optimally, to achieve better performancewith frequency filtering, a harder material should be used in the canalportion of the earplug. Further, to accommodate variations in phasedifferences between individuals with CANS dysfunction, differentfrequencies will be altered using acoustic filter elements within thecanal and by altering the acoustic impedance of the materialssurrounding the filter elements.

Commercially available filters are designed for wearing binaurally toreduce damaging noise while maintaining speech. It is not an intentionaleffect of the filter to produce a time delay in the acoustic signal.However, the inventors recognized that monaural use of such a filter wasa passive filter approach to inducing a BPTD. The modifications to thefilter to change the length of the filter were done on customtrial-and-error basis. The filter, with the resultant notched frequencyconfiguration at 2000-3000 Hz, when worn monaurally, has the effect of aBPTD. The proposed passive device would be designed specifically forinducing a BPTD, and could be designed to induce a predetermined BPTDobtained from the testing procedure described above. In addition, theBPTD could be limited to a particular frequency range (depending on PATresults) for specific amplitudes within the limitations of thecapabilities of passive filtering elements. This would provide theability to control the induced BPTD for individual fitting based on thediagnostic results. However, as mentioned earlier, the current art doesnot offer flexibility with size of BPTDs at specific frequencies foroptimal auditory and human performance enhancement.

In order to understand the time delay in a plug, it is necessary to usea model that includes the complex response characteristics of the ducts.This is similar to the familiar insertion loss calculations that areperformed in normal design; however, instead of only considering themagnitude of the response, the phase angle is also included. The modeldesign however can include significant simplifications due to the longwavelength of the sound relative to the diameter of the ear plug duct.

Note that unilateral muffing does not result in a BPTD due to thegradual attenuation across all frequencies (i.e., no selective notch).With the muffs, from 250 Hz to 6000 Hz there is a 5-10 dB attenuationper octave.

Speech recognition scores were obtained in the sound field with thesubject seated 3 feet from a front facing speaker. Monosyllabic wordswere presented at 40 dB SL re: sound field speech reception threshold inthe presence of broad band noise (s/n=+5) presented from a back speaker.

FIG. 13 shows speech recognition performance in noise for 22 individualswith CANS dysfunction. Five different conditions are shown in thefigure.

-   -   1. “no plug”: nothing in either ear.    -   2. “RE muffed: hearing protection muff (noise reduction rating        25 dB-ANSI S12.6) worn over right ear.    -   3. “LE muffed”: hearing protection muff (noise reduction rating        25 dB-ANSI S12.6) worn over left ear.    -   4. “unilatplug”: standard filtered earplug worn in one ear only.    -   5. “bilatplug”: standard filtered earplugs worn in both ears.

Of these five conditions, only condition 4 introduces a BPTD. Conditions2 and 3 result in unilateral noise reduction and condition 5 results inbilateral high frequency noise reduction. All differences arestatistically significant (p<0.05), except for the three conditions,which included the left ear muffed, and no plugs, bilateral plugging andno plugging, and left ear muffed and bilateral plugging. Of particularinterest is the significant improvement in speech recognition with aninduced BPTD (“unilat plug”), P<0.0001. Noise reduction without a BPTD(unilateral muff or bilateral earplugs) does not result in enhancedspeech recognition.

FIG. 14 shows speech recognition ability in noise results for 12individuals without CANS dysfunction. Five different conditions areshown in the figure.

-   -   1. “noplug”: nothing in either ear.    -   2. “RE muffed”: hearing protection muff (noise reduction rating        25 dB-ANSI S 12.6) worn over right ear.    -   3. “LE muffed”: hearing protection muff (noise reduction rating        25 dB-ANSI S12.6) worn over left ear.    -   4. “REplug”: standard earplug worn in right ear only.    -   5. “LEplug”: standard earplug worn in left ear only.

The “no plug” results are significantly (p<0.01) greater than any of theother conditions. These results demonstrate the importance ofsynchronous binaural processing of auditory input for enhanced speechdiscrimination in noise for individuals with a normal CANS. Furthermore,these results indicate that unilateral noise reduction (conditions 2 and3) or introducing a BPTD (conditions 4 and 5) do not enhance speechdiscrimination in noise for individuals with normal CANS function.

Note that speech discrimination results for the atypical group undercondition 1 (“no plug”) are significantly lower than those for thenormal group under condition 1 (“no plug”). Note also that undercondition 4 (“unilat plug”), the atypical group performs atapproximately the same level as the normal group does under condition 1(“noplug”).

Preliminary Data of BPTDs on Human Performance Using Electronic Device

Ten normal CANS subjects and 10 atypical CANS subjects were selected forvarious human performance testing using the prototype BPTD electronicdevice. The mean age of the 10 normal subjects was 31 years with an agerange of 21-43 years. In this group, five individuals were male and fivewere female. In the atypical CANS group, the mean age was 29.1 yearswith an age range of 15 to 47 years. Seven females and 3 males wereincluded in this group. All subjects in the two groups passed theinitial subject selection criteria. The ten subjects that were includedin the atypical CANS group failed at least one test in either ear in theCAP test battery. Further, to provide for a balancing of BPTDs for thenormal group, subjects for the atypical group were selected when theyshowed maximum improvement for the DBFT with a 2.5-7.5 msec BPTD toeither the right or left ear.

Another version of the DBFT (404 FIG. 4) was developed to includetime-lagged bisyllabic stimuli that were presented in 2.5 msecincrements (the previous DBFT used 5 msec increments). This versionincluded thirty bisyllabic words per list (4 lists) that were lagged intime between ears of 0 msec, 2.5 msec, 5 msec, and 7.5 msec and recordedin a CD format with an 8-talker babble (s/n ratio of +2 dB) embedded inthe background and presented binaurally. These words were presentedunder earphones at 40 dB sensation level relative to pure tone averagesfor both ears. The lag ear was determined by results from the DBFT 5msec version (404 FIG. 4). The highest speech recognition percent scorefor bisyllabic words was determined to be the “optimal” msec setting forthe BPTD device for atypical CANS subjects. The optimal condition fornormal CANS subjects was randomized at 2.5 msec, 5 msec, and 7.5 msec.Statistical analysis showed that these word lists were equivalent.

The 5 auditory conditions used in the preliminary studies were asfollows: (1) natural condition which was unoccluded with 8-talker babblepresented at 40 dB HL, (2) quiet which consisted of an unoccludedcondition with 8-talker babble presented at 25 dB HL, (3) optimalcondition using the BPTD electronic device in the presence of 40 dB HL8-talker babble; (4) 0 msec condition using the BPTD electronic devicewith 40 dB HL 8-talker babble, and (5) opposite BPTD (same setting butin opposite ear) from the optimal setting (e.g., if “optimal” was a 5msec lag to the right ear, then “opposite” is a 5 msec lag to the leftear). Not all tests examined condition 5.

Auditory Discrimination

Percent improvement in speech recognition ability using the BPTD devicewas assessed using four thirty-bisyllabic word lists that were recordedon a CD at 0 msec (408 FIG. 4). Auditory stimuli were presented in thesound field from a front facing speaker two meters from the individual.Test stimuli were presented at 45 dB sensation level (re: sound fieldspeech reception threshold) in the presence of an 8-talker babblerecorded at a +2 s/n ratio. Both stimuli were presented from the frontspeaker in a double-walled sound proof room.

Results (see FIG. 15) under these conditions showed a type effect acrossconditions (p=0.0039). There was also a condition effect (p=0.0474). Theatypical group showed the greatest percent improvement for speechrecognition ability with the BPTD device set at their “optimal” lagtime.

Motor

Gait studies were performed in a controlled uniform sound environment—asemi-anechoic chamber. Reverberation times were long enough (oramplitudes sufficiently low) that the room was taken as representativeof the sound field in an open or large room with high damping. Theambient sound level in the chamber was 45 dB SPL (Metrosonics dosimeter,Model dB307, Class Type 2A, Rochester, N.Y.). Sound sources were thenintroduced into the chamber under controlled amplitude anddirectionality. This is a highly controlled sound field relative to allprevious gait studies in the literature.

Speakers were placed in the anechoic chamber at 0 (far left), 45, 90(center), 135, and 180 (far right) locations in a clockwise directionrelative to the direction of travel. The five sound sources wererandomly presented to create the general localized sound condition (LS).Two additional cases were run in the chamber without speaker input:walking with and without earmuffs (Peltor, ModelH6A/V) created thegeneral reduced sound level condition (RS). For the BPTD device study,the center speaker was used.

The speaker output (i.e., sound source) was a tape-recorded eight-personmulti-talker babble presented at a sound level that was within three dBof a 56 dB SPL in the chamber calibrated gait area. To reduce theinfluence of visual stimuli, all materials used in the chamber weremonochromatic (i.e. either gray or black) and the room lighting wasreduced to approximately 0.9 foot candles (equivalent to a moderatelylighted parking lot).

A calibrated three-dimensional video gait analysis (Peak Motus,Englewood, Colo.) was completed with three camera views. The threecameras recorded each subject walking straight ahead within thecalibrated area at a comfortable pace for two strides. The subjectrepeated each condition until three to five gait cycles were recordedbetween consecutive heel strikes of the same foot. As part of the motionanalysis system, retro-reflective markers were mounted on the skin using3M™ hypoallergenic double-sided tape. On the head, two markers wereplaced on a spandex swim cap pointing upward directly above the ears.Body markers were placed on the vertebra prominens (C7 vertebra),shoulders, elbows, wrists, greater trochanters, knees, and ankles.

To normalize the gait data for subject stature, the kinematic data weredivided by the subject's height in meters. The following gait parameterswill be presented: walking speed (% height/sec), stride width (%height), and center of mass position (COM) (% height). The relative COM(COM Del) was the difference of the lateral COM position from the originbetween the first heel strike and the time of measurement. The Root MeanSquare Error (RMSE) method was used to calculate the mean lateraldeviation from a straight-line path of the COM.

A study was performed assessing gait while using the electronic deviceset at an optimal BPTD (Burleigh et al., 1999). Optimal BPTD wasdetermined by the DBFT results, (i.e. if a subject had the highest DBFTscore with a 5 msec delay to the right ear, a right 5 msec delay was the“optimal” setting). The BPTD device was used with 6 normal and 6atypical subjects in three different conditions: “optimal,” “0 msec” and“opposite” as described above.

FIGS. 16, 17, and 18 show the walking speed, stride width and RMSEresults for the atypical and normal groups under the different BPTDdevice conditions. The data graphically presents the differences inthese parameters between the three BPTD device conditions. For example,the first bar in FIG. 16 shows the average of the differences in walkingspeed for each of the atypical subjects between the “optimal” and “0msec” conditions.

It is evident that atypical group's gait is significantly improved (i.e.they walk faster) under both the “optimal” and “opposite” BPTDs,compared to the absence of a BPTD (0 msec), while the BPTD settings havelittle effect on the normal subjects' gait. The differences between theatypical and normal groups in the walking speed figure are not quitestatistically significant (p=0.074 for “optimal-0” and p=0.064 for“opposite-0”). Given the relatively small number of subjects in thisstudy, and large variation in gait parameters, this was not surprising.However, the trends are quite strong and with a larger number ofwell-matched (on gender and age) subjects, significant differences areexpected.

The results for stride width (FIG. 17) and Root Mean Square Error (RMSE)(FIG. 18) are similar, showing an improvement in gait (decrease instride width and RMSE) for the atypicals under both the “optimal” and“opposite ”conditions, and little effect on the gait of the normals. Thedifferences between the atypicals and normals for stride width were notstatistically significant for the “optimal-0” case (p=0.1042), but werefor the “opposite-0” case (p=0.0422). For RMSE (FIG. 18) the differencesbetween the atypicals and normals were not significant (p=0.1552 andp=0.1012, respectively for “optimal-0“and “opposite-0”).

The decrease in stride width and RMSE is seen as an improvement in gaitas the decreases tended to bring the values of these parameters for theatypicals closer to the values for the normals. While the gait of thenormal subjects was impacted very little by the device, as compared tothe atypical group, the graphs indicate a trend that the “optimal” and“opposite” BPTDs actually degrade the normal subjects' gait. This trendsupports the notion that while an induced BPTD in a normal CANS systemis disruptive, it can be accommodated.

It was surprising that the “optimal” and” opposite” settings both seemto enhance gait in the atypical group. Perhaps this is evidence thatwhile BPTDs impact gait, the effect is different from the impact ofBPTDs on other aspects of human performance, such as speechdiscrimination.

Interestingly, most changes in individual atypical subjects' gait underthe different BPTD device conditions were significant. For example, mostatypical subjects walked significantly faster under the BPTD device“optimal” setting when compared to their walking speed under the “0msec” setting, using multiple trials under each condition as themultiple measures.

Speech

Acoustic measures of diadochokinetic rate or maximum repetition rate fornon-speech material includes: duration in msec of 5 correct syllablesequences out of 7 consecutive utterances. This measure was used as anassessment of articulatory speed; however, because only correct syllableproductions were counted, it probably more accurately reflectedarticulatory efficiency. Syllable and pause durations were also measuredas were irregularities or variances among successive syllable and pausedurations within each condition.

Results of performance of these tasks under auditory conditions innormal and atypical subjects revealed statistically significantdifferences in articulatory efficiency, syllable duration and variancesin syllable and pause duration when comparing those persons with normaland atypical CANS function (p<0.05 for each). This suggested that whileall subjects were considered normal speakers, differences in abilitiesto make rapid alternating movements differ in persons with atypicalversus normal CANS function.

There was also a statistically significant difference in articulatoryefficiency and intersyllabic pause durations among experimental auditoryconditions for both groups (p<0.05). Durations for completions of 5accurate syllable sequences and intersyllabic pauses were shorter underthe optimal or accommodating auditory condition compared to conditionsof 0 msec delay or reduced noise. These findings suggest that not onlydo auditory conditions impact the performance of rapidly alternatingnon-speech movements, but that specific adjustments in binaural timingbetween ears may improve performance over conditions where nodifferences are introduced.

In oral reading of an 85-word paragraph, perceptual measures were takenof the number of dysfluencies and reading speed in words per second.Perceptual dysfluency types included: part and whole word repetitions,phrase repetitions/restarts, prolongations, phonatory disruptions,interjections, blocks, and pauses. This system of dysfluencyclassification was modified from Kent, 1994.

A review of the number of dysfluencies in oral reading provided the mostconvincing evidence of benefits of accommodating BPTDs. While there werestatistically significant differences in the total number ofdysfluencies between normal and atypical experimental groups (p<0.05),for this parameter there was also a statistically significantcondition-type interaction (p<0.05) suggesting that the differences inperformance in favor of the normal subjects was a function of theauditory condition. Specifically, as can be seen in FIG. 19, not only dothe persons without CANS dysfunction show a flatter profile ofperformance across auditory conditions when compared with those withCANS deficits, those with atypical CANS function make the fewest errors,performing very close to normal at their optimal or accommodatedauditory condition. In fact, statistically significant differences areapparent between normals and atypicals under natural and 0 msecconditions but are not at the accommodating condition. Further, theperformance of atypicals in pairwise condition comparisons, revealsstatistically fewer dysfluency errors made under optimal oraccommodating auditory condition when compared against each: 0 msec,natural and reduced noise conditions.

Reading speed as measured by words per second in an 85-word oral readingsample revealed statistically significant differences when comparingthose persons with normal and atypical CANS function (p<0.05). It shouldalso be noted that although statistically significant differences werenot observed in pairwise comparisons across auditory conditions for thesubjects with atypical CANS function, the fastest reading rate conditionfor this group was their optimal or accommodated condition.

The foregoing discussion of the invention has been presented forpurposes of illustration and description. Further, the description isnot intended to limit the invention to the form disclosed herein.Consequently, variations and modifications commensurate with the aboveteachings, within the skill and knowledge of the relevant art, arewithin the scope of the present invention. The embodiment describedhereinabove is further intended to explain the best mode presently knownof practicing the invention and to enable others skilled in the art toutilize the invention as such, or in other embodiments, and with thevarious modifications required by their particular application or usesof the invention. It is intended that the appended claims be construedto include alternative embodiments to the extent permitted by the priorart.

1. An apparatus for compensating for a measured binaural phase timedelay profile (BPTD) of an individual comprising: means (704) fordelaying sound signals to an ear of the individual according to theBPTD; and means (706) for applying different phase shifts at differentfrequencies according to the BPTD.
 2. The apparatus of claim 1, whereinthe means for delaying comprises a passive earplug (1000) having ducting(1002) which delays propagation of sound relative to air.
 3. Theapparatus of claim 2, wherein the means for applying phase shiftscomprises at least one acoustical filter element (1004) within the earplug.
 4. The apparatus of claim 2, wherein the ducting is fluid filled.5. The apparatus of claim 1, wherein the means for delaying soundsignals and the means for applying phase shifts are implemented as anelectronic hearing aid (600).
 6. The apparatus of claim 5, wherein thehearing aid is a digital hearing aid and further wherein the apparatusincludes: an analog to digital converter (ADC) (606); a digital signalprocessor (DSP) (608); and a digital to analog converter (DAC) (610) theDSP implementing the means for delaying and the means for applying phaseshifts.
 7. The apparatus of claim 6, wherein the means for implementingphase shift profile comprises a FIR filter (806).
 8. The apparatus ofclaim 6, wherein the DSP implements other audio signal processing (808)as well as the means for delaying sound signals and the means forapplying phase shifts.
 9. The apparatus of claim 8, wherein the otheraudio processing implemented includes noise reduction.
 10. The apparatusof claim 8, wherein the other audio processing implemented includesapplying amplitude changes to the sound signals.
 11. The apparatus ofclaim 1, further including means (616) for modifying the means forapplying phase shifts according to environmental conditions.
 12. Amethod of compensating for a measured binaural phase time delay profile(BPTD) of an individual comprising the steps of: delaying (804) soundsignals to an ear of the individual according to the BPTD; and applyingdifferent phase shifts (806) at different frequencies according to theBPTD.
 13. The method of claim 12, further including the step (808) ofapplying amplitude modifications at different frequencies.
 14. Anapparatus to compensate for a measured binaural phase time delay profileof an individual comprising: a sound signal delay element according tothe binaural phase time delay profile; and a frequency differing phaseshift element according to the binaural phase time delay profile. 15.The apparatus of claim 14, wherein the sound signal delay elementcomprises a passive earplug having ducting which delays propagation ofsound relative to air.
 16. The apparatus of claim 15, wherein thefrequency differing phase shift element comprises at least oneacoustical filter element within the ear plug.
 17. The apparatus ofclaim 14, wherein the sound signal delay element and the frequencydiffering phase shift element are implemented as an electronic hearingaid.
 18. The apparatus of claim 17, wherein the hearing aid is a digitalhearing aid and further wherein the hearing aid comprises: an analog todigital converter element; a digital signal processor element; and adigital to analog converter element the digital signal processor elementimplementing the sound signal delay element and the frequency differingphase shift element.
 19. The apparatus of claim 18, wherein thefrequency differing phase shift element comprises a FIR filter.
 20. Theapparatus of claim 18, wherein the digital signal processor elementimplements other audio signal processing as well as the sound signaldelay element and the frequency differing phase shift element.
 21. Theapparatus of claim 20, wherein the other audio processing implementedincludes noise reduction.
 22. The apparatus of claim 20, wherein theother audio processing implemented includes applying amplitude changesto the sound signals.
 23. The apparatus of claim 14, further comprisingan environmental conditions modification element to which the frequencydiffering phase shift element is responsive.